The Federal Motor Vehicle Safety Standard (FMVSS) 108 for on-road vehicle lighting requires headlamps to generate high beam and low beam patterns defined by an array of points at each of which the beams are required to have an intensity within a specified range. Typically, high beams and low beams provided by a headlamp are achieved using one incandescent light source with a reflector designed to generate a high beam, and another such light source with a reflector designed to generate a low beam. In such headlamps then, two different incandescent light sources and two different reflectors are used to generate the two beam patterns.
The FMVSS requirements do not specify the brightness of headlamps for off-road applications because there is no concern about headlamp glare blinding other drivers off-road; thus off-road headlamps can have much higher light intensities than allowed by FMVSS 108.
It would be useful to have a headlamp that can provide a high beam or a low beam for on-road use, and yet can easily switch to a mode in which illumination is provided suitable for off-road use. It would be further desirable to have a headlamp that minimizes the number of internal components to achieve both an on-road and off-road headlamp, so as to reduce costs.